Canada thistle (Carduus arvensis). Perennial. The plant should never be allowed to produce seeds, and the underground stems, which are usually 3 to 12 inches under ground, must be removed or starved by covering with straw. Cutting the plants just before the budding period is destructive. To eradicate by cutting or cultivation no plant should be allowed to show green leaves for a period exceeding a few days. The most effective spray is sodium arsenite, 11/2 to 2 pounds per 52 gallons water; or common salt, 1/3 to 1/2 barrels to 52 gallons water; or copper sulfate, 15 pounds to 52 gallons water; or iron sulfate, 75 pounds to 52 gallons of water, sprayed on twice, one week apart. Spray just before the budding period. Spray again after the crop is harvested. Repeat the second year. Sodium arsenite is a very active poison, and must be used with care.
Dandelion (Taraxacum officinale). Perennial. Cutting below ground is effective. Keep lawn heavily seeded to crowd out the dandelion. Spray with iron sulfate, 11/2 to 2 pounds for each gallon of water. Spray two or three days after mowing lawn, and do not again mow until two or three days after spraying. Spray on bright, sunshiny days. Heavy wetting within two days after spraying destroys the weed-killing power. Spray at intervals of four to six weeks.
New York State Station (Geneva) reports, 1911, that spraying dandelions with iron sulfate was not successful. The second season of treatment the grass was considerably injured.
Sow-thistle (Sonchus arvensis). Perennial. Spraying is not effective. Practice bare cultivation for two seasons, allowing no green leaves to appear. On small patches, smother by covering with straw or manure. There are annual species of Sonchus.
Quack-grass (Agropyron repens). Perennial. In small patches, uproot in dry, hot weather and remove all underground stems. Cut off closely in July, and smother with straw or manure. In large areas, mow when in blossom, and break the sod shallow in mid-July. Backset in mid-August slightly deeper than before. Disc and harrow throughout the fall, allowing no green leaves to show. Then plow deeply in late fall. Plant cultivated crop next season, and dig out every blade of grass. Or sow a heavy seeding of millet or other dense-growing annual forage late in May on a well-prepared seed bed. The drier the ground and the hotter the weather, the better the killing effect of cultivation.
White daisy, White-weed (Chrysanthemum Leucanthemum). Perennial. Plow up old infested meadows. Spray with iron sulfate at rate of 150 to 200 pounds per acre. Spray when blossom stalks are just forming. Two or more years are required for eradication. (R. I. Sta.).
Black mustard (Brassica nigra) and wild mustard (B. arvensis). Annual. Spray with iron sulfate, 50 gallons to acre, using 75 to 100 pounds of iron sulfate, depending on whether the plants are tender and succulent or more mature and hardy.
Orange hawkweed (Hieracium aurantiacum), chickweed (Stellaria media), and some other of the shallow-rooted succulent weeds of lawns and grass lands can be combated effectively by the use of salt, more so than by any other chemical. Fine, dry salt should be applied on a bright, hot summer day (late June or early July best), broadcasting it so as to cover all plants uniformly, since it kills chiefly by drawing water from the leaves. One to four quarts of salt can be used per square rod, with little or no permanent injury to the grass if on a strong soil in the northeastern states. Since the effect varies with local conditions, advance trials should be made on small scale. Following the application, the dead weeds should be raked out and a liberal application of grass-seed made.